When data is communicated between a base station of a wireless communication network and a User Equipment (UE) served by the base station, a Radio Link Control (RLC) protocol can be applied as a sub-layer of Layer 2 for handling this data communication, which has been specified by the Third Generation Partnership Project (3GPP). RLC is typically implemented by using data receiving and transmitting RLC entities in both the base station and the UE. The RLC entities are configured to exchange data in the form of Service Data Units (SDUs) of a higher layer over a logical channel configured by the so-called Radio Resource Control (RRC) layer. On a lower layer called the Medium Access Control (MAC) layer, such logical channels are mapped to transport channels where the data is communicated in the form of data blocks, which communication is controlled by a so-called MAC-scheduler.
At the RLC level, an SDU may further be segmented into multiple smaller chunks of data, referred to as Protocol data Units (PDUs), before transmission, which are put together again at the receiving side. Depending on the communication service used and/or current traffic situation, it may be required that reception of the transmitted PDUs is confirmed by means of PDU status reports sent from the data receiving RLC entity in one node to the data transmitting RLC entity in an opposite node. This can be applied for both downlink and uplink communication of data. If a status report indicates that a PDU has not been received properly, or if no status report has been received at all for that PDU, the data transmitting RLC entity is typically configured to re-transmit the same PDU, which may be repeated a number of times e.g. until a status report is received from the data receiving RLC entity indicating that the PDU has been received properly.
The RLC entities can be configured to apply different communication modes referred to as Transparent Mode (TM), Unacknowledged Mode (UM) and Acknowledged Mode (AM). Which mode to use for a session is decided by a radio bearer mapping function at the base station, typically based on the type of service used and possibly also on the available resources, and the selected mode is signalled from the base station to the UE at establishment of a radio bearer, referred to as “radio bearer setup”.
In TM, the SDUs are communicated “as is” between the RLC entities in the base station and the UE and no additional processing or reception control is made whatsoever. In UM, the SDUs are first segmented into PDUs at the data sending RLC entity before transmission of the PDUs one by one, and the PDUs are then joined together to reassemble the SDUs again at the data receiving RLC entity. Thereby, the PDU size can be selected freely independent of the SDU size, providing flexibility to the lower layers. No status reporting is required or expected for UM and any PDU that has not been received properly will be missed or discarded at the receiving side.
In AM, PDUs are communicated as in UM but acknowledgement of reception of the PDUs is expected at the data receiving RLC entity in the form of the above-described PDU status reports, which is also referred to as Automatic Repeat reQuest (ARQ). It should be noted that the MAC layer typically also applies a similar acknowledgement mechanism called Hybrid ARQ (HARQ) to confirm reception of data blocks.
In FIG. 1, a base station 100 is schematically shown comprising a data receiving RLC entity 100a and a data transmitting RLC entity 100b. Further, a UE 102 served by base station 100 comprises a data receiving RLC entity 102a which can receive data, e.g. PDUs, from the data transmitting RLC entity 100b, and a data transmitting RLC entity 102b which can transmit data, e.g. PDUs, to the data receiving RLC entity 100a. 
With this configuration, data in the form of PDUs may be sent on an uplink channel from the data transmitting RLC entity 102b to the data receiving RLC entity 100a. In that case, corresponding PDU status reports may be sent on an opposite downlink channel from the data receiving RLC entity 100a to the data transmitting RLC entity 102b, such as when the above AM is used, as shown in the figure. Correspondingly, PDUs may also be sent on a downlink channel from the data transmitting RLC entity 100b to the data receiving RLC entity 102a. In that case, PDU status reports may be sent on an opposite uplink channel from the data receiving RLC entity 102a to the data transmitting RLC entity 100b. 
There are some drawbacks associated with the above AM RLC procedure. Since the ARQ process at RLC level must basically wait for the HARQ process at MAC level to be completed, the re-transmission process at RLC level takes considerably longer than the HARQ re-transmissions, which could delay the communication to a great extent especially if re-transmissions on the RLC layer occur frequently. Another difference is that in HARQ re-transmissions, the multiple transmissions of the same data block can be combined for decoding that data block at the receiver, using so-called soft combining, which is not employed for PDUs at the RLC level. In the latter case, all failed transmission attempts are thus of no use and a total waste of resources. As a result, the AM mode for RLC is selected only for delay-tolerant services.
A problem with the AM RLC procedure is that status reports sometimes do not arrive on time or not at all to the data transmitting node, resulting in re-transmission of the same data since that data has not been acknowledged by the data receiving node, at least as perceived by the data transmitting node. This situation may occur even when the data has in fact been conveyed and received successfully and the status reports have been sent but not delivered properly, for some reason.
Status reports can be delayed or missed repeatedly resulting in repeated re-transmissions of data. Eventually, it may even be determined that the current radio link used for data is apparently not good enough and must be torn down and replaced by a new radio link, which is a time-consuming and resource-demanding process. If the radio link for data was perfectly acceptable in spite of the missing status reports, the process of tearing down the link and setting up a new connection will be made unnecessarily. The delay of status reports, if required or expected, can thus lead to excessive re-transmissions of data which will cause increased load in the cell, delays and impaired quality of the communication as well as needless tear-down and re-establishment of radio link.